The Etek 4 is a great marker. Think half-way between Ego9 and Ego10. You dont get an OLED board, but the settings arent that difficult to mess with. It has a good barrel, good cure bolt, a great reg and easy on/off asa. As usual with the ETEK line though, it is as loud as a cannon. And I have never been a fan of PE's finger detents. They seem to snap way to often.
The FX is a decent marker. If it were stock, I would tell you to stay away and go with the ETEK. However, the HUSH bolt and LAW ram, quiet it down a good bit. The RAM will soften the shot and ping. The switchblade trigger is nice, but a little bulky to me. The reg is easy to work on and the RAPS Asa is my favorite asa in the industry right now. The OLED board will take a bit to figure out the programming, but it has a ton of modes you can mess with.
Final Judgement (including the mods to the FX):
Trigger - ETEK
Barrel - ETEK
Bolt - FX
RAM - FX
Board - DRAW (imo)
Reg - ETEK
ASA - FX
Noise - FX (simply because of the hush bolt and LAW ram)
REMEMBER!!! This is all my own personal opinion. Your best bet is to find anyone that may have the 2 markers near you and shoot them for yourself.
Sic gorgiamus allos subjectatos nunc.